1. Field of the Invention
The present invention relates to ribs for an image display medium, which are employed in, for example, a display such as a plasma display panel (PDP), an electroluminescent display element (EL) or the like or a particle driving-type image display medium such as electronic paper which employs an image display material with electrophoreticity, thermal rewritability, electrochromy or the like, or the like, and relates to a process for fabricating the ribs and to an image display medium which utilizes the ribs.
2. Description of the Related Art
Heretofore, ribs have often been utilized in the field of image display media. In plasma display panels (PDP) and electroluminescence (EL) displays, ribs are utilized for maintaining inter-substrate (electrode) gaps and preventing pixel smearing, and as fluorescent substance and luminescent substance coating surfaces. Further, in particle-driving type image display media such as electronic paper and the like, ribs are required for preventing particle sinkage.
For these ribs, stripe-form arrangements have been employed, in view of ease of fabrication. Specifically, the following processes have all been tried: a photolithography process for etching a dry film (a resist material) (Japanese Patent Application Laid-Open (JP-A) No. 7-43692); a sandblasting process utilizing a resist material (JP-A No. 5-297810); in view of recent concern for the environment, a process of screen printing which utilizes a printing ink, which does not produce waste (JP-A No. 8-304805); and the like.
The prior technologies described above are all for stripe-form ribs. However, pixels of many image display media are formed in grid patterns. Therefore, with regard to image quality, meaning prevention of light emission leakage, particle sinkage and lateral flows, it is desirable to form ribs so as to make a lattice-form arrangement or the like, for example, so as to make a cell-form arrangement in which each pixel is two-dimensionally enclosed by the ribs.
It is ideal for ribs to be in a cell-form arrangement including a lattice pattern, because strength for maintaining an inter-substrate (electrode) gap is improved, surface area for coating a fluorescent substance or luminescent substance can be made larger, brightness is improved, reductions in power consumption are enabled, and so forth.
With ribs in such a cell-form arrangement, an area of an image display surface that the ribs occupy is larger than with a stripe-form arrangement. Therefore, there is a problem in that an open area ratio of the image display medium is reduced. In order to solve this problem, it is necessary to make the ribs thinner.
However, with photolithography utilizing a dry film, because of exudation of an etching solvent, defects will occur frequently if the ribs are made thinner. Further, with a sandblasting process utilizing a resist material, if the ribs are made thinner, lateral impacts from blasting particles cannot be disregarded, and rib defects are likely to occur frequently.
Further yet, when making ribs narrower is attempted with screen printing utilizing printing ink, there is a problem with stripe-form ribs in that the ink sags and lower portions of the ribs are fatter. If production of cell-form ribs is attempted, the ink will amass at intersection points. As a result, the ribs will become higher just at the intersection points, and functionality of the ribs will be lost.